In the conventional art, in order to effectively use solar energy, a photovoltaic thermal hybrid solar collector that obtains electricity and heat is commercially available and is introduced to general houses. Energy efficiency of a photovoltaic thermal collector is about 20% at most, and 80% of solar energy is heat. The energy efficiency of the photovoltaic module is only 20%; however, heat collection efficiency is about 50%. Hence, a photovoltaic thermal collector having the heat collection efficiency has been actively studied for 20 years.
Regarding photovoltaic power generation, a system that has solar panels installed on a roof of a house and meets a household power demand has been put to practical use. In addition, as for solar thermal power generation, generation from solar heat as a heat source through thermoelectric conversion using a thermoelectric conversion element having the Seebeck effect has been known.
However, a photovoltaic power generation system has problems in that solar energy density is not only low on the earth's surface, but also is likely to vary depending on the influence of weather conditions or sunshine duration. In other words, arises a problem that the influence makes it difficult to stably obtain power. In addition, in a solar thermal power generation system using the thermoelectric conversion elements, currently-known thermoelectric conversion elements have low performance, and there arises a problem that it is difficult to obtain sufficient power generation efficiency.
Japanese Unexamined Patent Publication No. 2007-81097 (Patent Document 1) and Japanese Unexamined Patent Publication No. 2001-7412 (Patent Document 2) propose a photovoltaic thermal collector that is capable of efficiently using solar energy. Specifically, the patent documents propose in the photovoltaic thermal collector: a solar panel is combined with a solar thermal electric generation apparatus having thermoelectric conversion elements that convert thermal energy from sunlight into electrical energy. According to the photovoltaic thermal collector, the solar thermal energic generation apparatus compensates for shortcomings that generation efficiency is likely to be influenced by conditions of cloudy weather, night time or the like; and the solar panel compensates for shortcoming that generation efficiency of the thermoelectric conversion elements themselves is not enough. Patent Document 1 discloses that it is possible to stably obtain higher power by about 5% or higher and 15% or lower than an amount of power obtained in a configuration including only the solar panel.
However, in the photovoltaic thermal hybrid photovoltaic thermal collector disclosed in Patent Document 1, since the solar thermal power generation is performed through power generation by the thermoelectric conversion elements, power obtained from the solar thermal power generation is normal. Hence, the photovoltaic thermal collector is considered only as a technology of compensating for defect of solar panels for a household or an office building. Nowadays, there is a demand for technology that compensates for power shortage without building a new nuclear power plant. In this respect, the technology disclosed in Patent Document 1 is not sufficient for the demand.
Herein, a photovoltaic thermal hybrid power generation system through collection or semi-collection of light is being considered. For example, such a system or the like includes: a light collecting mirror provided with an infrared reflective film formed on a front surface thereof; a heat collecting portion that collects infrared rays reflected on the infrared reflective film on the front surface of the light collecting mirror; a generator provided with a turbine that rotates by steam generated with heat collected by the heat collecting portion; and a solar panel including photovoltaic cells disposed inside the light collecting mirror. The system or the like is large-sized equipment and is very expensive.
A thermal photovoltaic hybrid product which has been practically studied so far is made of a solar panel and a conventional hot-water panel stuck each other. Therefore, a problem such as copper-pipe corrosion or water leakage remains as is.
A light collecting type has good thermal efficiency; however, an initial investment amount is high, an installation space is large, and thus there are many problems that need to be solved for a widespread use of the type.
[Patent Document 1] Japanese Unexamined Patent Publication No. 2007-81097
[Patent Document 2] Japanese Unexamined Patent Publication No. 2001-7412